1. Field of the Invention
The present invention relates, in general, to an apparatus for measuring the thickness of an oxide layer formed on a cladding of each fuel rod of a nuclear fuel assembly using an eddy current sensor and, more particularly, to an apparatus for measuring the thickness of an oxide layer of a fuel rod, which includes driving means for providing movement in upward and downward, forward and backward, and leftward and rightward directions, a first probe for testing claddings of fuel rods placed in an outer side of a nuclear fuel assembly (hereinafter, “outer fuel rods”), and a second probe for testing claddings of fuel rods placed in an inner side of the nuclear fuel assembly (hereinafter, “inner fuel rods”).
2. Description of the Related Art
During operation of a nuclear reactor, fuel rods disposed on each nuclear fuel assembly are immersed in a coolant/moderator in a reactor core. In light water reactors using zirconium or zircaloy cladding tubes for fuel rods, zirconium oxide (zirconia) is deposited on the fuel rods at a thickness of about 100 μm by a reaction between a coolant/moderator using water and zirconium in the cladding tubes. An adverse effect caused by the zirconia produced when heat is being transferred from the fuel rod cladding tube to the coolant/moderator and a metal loss which damages the structural integrity of the cladding tube, cause the thickness of the cladding tube to be reduced. As such, a restriction is placed on the maximum amount of oxide allowable to each fuel rod. Once the amount of oxide reaches this limit, the fuel rod must be replaced.
Thus, the thickness measurement of the oxide layer is important for accurately evaluating the thermohydraulic performance of the fuel rod, estimating operational restrictions of the fuel rod, and estimating the longevity of the fuel rod.
Generally, the thickness of the oxide layer of the fuel rod is measured by eddy current testing, and the damage to the fuel rod is checked by ultrasonic testing.
Examples of the related art for measuring the thickness of the oxide layer of the fuel rod using eddy current testing include Korean Registered Utility Model No. 20-0339313, entitled “The probe fixture for eddy current testing of the RCCA of nuclear fuel type,” Korean Patent Application Publication No. 10-2004-0012065, entitled “Transfer apparatus of nuclear fuel rod for eddy current testing,” Korean Patent No. 10-0735213, entitled “Method for measuring oxide thickness underlying a ferromagnetic material on nuclear fuel rods,” and so forth.
However, the eddy current testing disclosed in the related art requires much time to do a test because the nuclear fuel assembly should be disassembled and fuel rods disassembled from the nuclear fuel assembly should be tested one by one. As such, it cannot efficiently test the oxide layers of the fuel rods.